Ex-situ nitrogen-doped porous carbons as electrode materials for high performance supercapacitor

Heteroatom co-doped green pea peel-derived biochar for high-performance energy storage applications

Green pea peel (GPP) is a waste, and it is abundant and available to be used for biochar synthesis. GPP-derived biochar (GP) is used vastly in wastewater treatment. Moreover, heteroatom co-doping of GP could be better than its single-doped and undoped in enhancement of active sites and conductivity, and in developing electrodes for supercapacitor applications. However, uncontrolled heteroatom co-doping clogs the pores in the biochar and stops the electrolyte from penetrating the porous structure, which results in reduced capacitance and higher resistance in the biochar. This study presented the controlled synthesis of GP, nitrogen (N)-doped biochar (NGP), and N and sulfur (S) ex situ co-doped GP (NSGP) through carbonization and chemical activation. As revealed by the characterization techniques, the synthesized GP, NGP, and NSGP are nanosheets with amorphous structures and defective structures. The specific capacitance of the NSGP-based electrode material, as determined by electrochemical characterizations, is 257.01 F g-1, more than the 230.22 F g-1 and 208.78 F g-1 of NGP and GP at 1 A g-1, respectively. The assembled NSGP//NSGP supercapacitor device has an 80.25 F g-1 specific capacitance at 1 A g-1, an energy density of 13.87 W h kg-1, and a 500 W kg-1 power density with a 99.46% capacity retention after 5000 cycles at 5 A g-1. It demonstrates that NSGP has better electrochemical performance than NGP and GP because of the improved active sites and conductivity.

Optimized mesopore design in ginkgo nuts-derived hyper-crosslinked porous carbon for enhancing supercapacitor capacitance performance

The capacitance performance of a co-doped carbon-based supercapacitor derived from Ginkgo nuts was significantly enhanced by optimizing the mesoporous structure through high-temperature pyrolysis combined with KOH activation. The precisely engineered GBHHPC-750-4 is characterized by a hyper-crosslinked 3D hierarchical porous structure, with an exceptionally high specific surface area of 3163.9 m2/g, a substantial mesopore proportion (Vmeso/Vt = 74.1 %), a broad pore size range of 2-10 nm, and elevated levels of heteroatom doping (3.4 at.% N, 8.3 at.% O, 1.6 at.% P). The symmetric supercapacitor based on the GBHHPC-750-4 electrode exhibits a peak specific capacitance of 256 F/g at 1 A/g, achieves an energy density of 118.2 Wh kg-1, maintains an impressive rate capability of 63.6 % across a wide current range (0.5-20 A/g) and demonstrates a prolonged cycle lifespan with 88.0 % capacitance retention after 5000 cycles in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMBF4) electrolyte, emphasizing the substantial potential of the optimized mesoporous carbon material for energy storage applications.

Versatile waste wood-chitosan composites for 2,4-D and paraquat adsorption: Isotherm modelling and thermodynamic evaluation

2,4-dichlorophenoxy acetic acid (2,4-D) and 1,1-dimethyl-4,4-bipiridinium chloride (paraquat) are among the most widely used herbicides and are known to be toxic. Fabrication of green adsorbents which are capable of removing both herbicides remains a challenge. Here, we fabricate a novel adsorbent from tropical waste wood and use a facile, chitosan-mediated N-heteroatom functionalization technique to augment surface nitrogen and improve specific surface area. The addition of 20 wt% chitosan to the waste wood feedstock prior to activation, increased specific surface area by 300 m2/g (∼25%) and nitrogen content by 7-fold. This functionalized material removed 69% of 2,4-D and 82% of paraquat at initial concentrations of 4 ppm and 40 ppm from model solutions at pH 7. It also removed 39% 2,4-D and 93% paraquat from binary mixtures demonstrating its versatility. 2,4-D adsorption increased with chitosan addition suggesting synergistic effects between protonated amine functions and the anionic herbicide form. Paraquat adsorption was negatively correlated with chitosan addition, implying antagonistic interaction between protonated amine functions and quaternary nitrogen atoms on herbicide molecules. Adsorption of both herbicides was spontaneous, entropically favored and exothermic with ΔG °: 19.2 kJ/mol and -28.8 kJ/mol; ΔS °: 7.42 and 28.6 J/Kmol and ΔH °: 17.0 kJ/mol and -20.1 kJ/mol for 2,4-D and paraquat respectively. Chitosan addition therefore provides a facile and green alternative for N-heteroatom functionalization, and these nitrogen-doped materials are promising candidates for the removal of multiple herbicides from aqueous systems.

Crafting the architecture of biomass-derived activated carbon via electrochemical insights for supercapacitors: a review

Escalating energy demands have often ignited ground-breaking innovations in the current era of electrochemical energy storage systems. Supercapacitors (SCs) have emerged as frontrunners in this regard owing to their exclusive features such ultra-high cyclic stability, power density, and ability to be derived from sustainable sources. Despite their promising attributes, they typically fail in terms of energy density, which poses a significant hindrance to their widespread commercialization. Hence, researchers have been exploring different cutting-edge technologies to address these challenges. This review focuses on biomass-derived activated carbon (BDAC) as a promising material for SCs. Initially, the methodology and key factors involved in synthesising BDAC, including crafting the building blocks of SCs, is detailed. Further, various conventional and novel material characterization techniques are examined, highlighting important insights from different biomass sources. This comprehensive investigation seeks to deepen our understanding of the properties of materials and their significance in various applications. Next, the architectural concepts of SCs, including their construction and energy storage mechanisms, are highlighted. Finally, the translation of the unravelled BDAC metrics into promising SCs is reviewed with comprehensive device-level visualisations and quantifications of the electrochemical performance of SCs using various techniques, including cyclic voltammetry (CV), galvanostatic charge-discharge test (GCD), electrochemical impedance spectroscopy (EIS), cyclic tests (CT), voltage holding tests (VHT) and self-discharge tests (SDT). The review is concluded with a discussion that overviews peanut-shell-derived activated carbon as it is a common and promising source in our geographical setting. Overall, the review explores the current and futuristic pivotal roles of BDAC in the broad field of energy storage, especially in SC construction and commercialisation.

Structural Regulation and Performance Enhancement of Carbon-Based Supercapacitors: Insights into Electrode Material Engineering

The development of carbon-based supercapacitors is pivotal for advancing high energy and power density applications. This review provides a comprehensive analysis of structural regulation and performance enhancement strategies in carbon-based supercapacitors, focusing on electrode material engineering. Key areas explored include pore structure optimization, heteroatom doping, intrinsic defect engineering, and surface/interface modifications. These strategies significantly enhance electrochemical performance through increasing surface area, improving conductivity, facilitating charge transfer, introducing additional pseudocapacitive reactions, and optimizing the density of states at the Fermi level, among other mechanisms. After introducing these fundamental concepts, the review details various preparation methods and their effects on supercapacitor performance, highlighting the interplay between material structure and electrochemical properties. Challenges in scaling advanced fabrication techniques and ensuring the long-term stability of functionalized materials are discussed. Additionally, future research directions are proposed, emphasizing the development of cost-effective, scalable methods and interdisciplinary approaches to design next-generation supercapacitors, thereby meeting the growing demand for efficient and sustainable energy storage solutions.

High electrochemical performance of nickel cobaltite@biomass carbon composite (NiCoO@BC) derived from the bark of Anacardium occidentale for supercapacitor application

Biomass carbon-based materials are highly promising for supercapacitor (SC) electrodes due to their availability, environment-friendliness, and low cost. Herein, an easy energy-saving hydrothermal process was used to produce NiCo2O4/NiOOH (NiCoO) composites with biomass carbon (BC) derived from the bark of Anacardium occidentale (AO) at different synthesis time durations (2 h, 4 h, 8 h, 16 h). The structural and morphological properties of the samples were analysed using XRD, Raman spectroscopy, XPS, SEM, TEM and BET, and the results exhibit the presence of carbon inserted into the nickel-cobalt hydroxide matrix. The NiCoO@BC composite synthesized in 4 h (NiCoO@BC(4 h)) displays a good specific capacitance of 475 F g-1 at 0.5 A g-1 and a low equivalent series resistance (ESR) value of 0.36 Ω. It shows a good coulombic efficiency of 98% and retains 86% of the capacitance after 4000 cycles. The asymmetric supercapacitor (ASC) device (NiCoO@BC(4 h)//AC) assembled using activated carbon (AC) as a negative electrode displays 20 W h kg-1 energy density and 900 W kg-1 power density at 1 A g-1. The stability test shows a good coulombic efficiency of 99% and 78% capacitance retention after 15 000 cycles. These findings imply that NiCoO@BC composites have outstanding electrochemical properties, making them suitable as SC electrode materials.

Nitrogen-Doped Cellulose-Derived Porous Carbon Fibers for High Mass-Loading Aqueous Supercapacitors

Biomass-based porous carbon with renewability and flexible structure tunability is a promising electrode material for supercapacitors. However, there is a huge gap between experimental research and practical applications. How to maintain good electrochemical performance of high mass-loading electrodes and suppress the self-discharge of supercapacitors is a key issue that urgently needs to be addressed. The structure regulation of electrode materials such as heteroatom doping is a promising optimization strategy for high mass-loading electrodes. In this work, nitrogen-doped cellulose-derived porous carbon fibers (N-CHPCs) were prepared by a facile bio-template method using cotton cellulose as raw material and urea as dopant. The prepared N-CHPCs have high specific surface area, excellent hierarchical porous structure, partial graphitization properties and suitable heteroatom content. The assembled high mass-loading (12.8 mg cm-2 ; 245 μm) aqueous supercapacitor has excellent electrochemical performance, i. e., low open-circuit voltage attenuation rate (21.39 mV h-1 ), high voltage retention rate (78.81 %), high specific capacitance (295.8 F g-1 at 0.1 A g-1 ), excellent area capacitance (3.79 F cm-2 at 0.1 A g-1 ), excellent cycling stability (97.28 % over 20,000 cycles at 1.0 A g-1 ). The excellent performance of high mass-loading N-CHPCs is of great significance for their practical applications in advanced aqueous supercapacitors.

N-Doped celery-based biomass carbon with tunable Co3O4 loading for enhanced-performance of solid-state supercapacitors

N-doped celery-based biomass carbon with tunable Co3O4 loading is prepared and shows enhanced specific capacitance.

Biomass-derived O, N-codoped hierarchically porous carbon prepared by black fungus and Hericium erinaceus for high performance supercapacitor

Biomass-derived carbon materials have been widely researched due to their advantages such as low cost, environmental friendliness, readily available raw materials. Black fungus and Hericium erinaceus contain many kinds of amino acids. In this paper, unique O, N-codoped black fungus-derived activated carbons (FAC X ), and Hericium erinaceus-derived activated carbons (HAC X ) were prepared by KOH chemical activation under different temperatures without adding additional reagents containing nitrogen and oxygen functional groups, respectively. As electrode materials of symmetric supercapacitors, FAC2 and HAC2 calcined at 800 °C exhibited the highest specific capacitance of 209.3 F g-1 and 238.6 F g-1 at 1.0 A g-1 in the two-electrode configuration with 6.0 M KOH as the electrolyte, respectively. The X-ray photoelectron spectroscopy confirmed that the as-synthesized FAC X and HAC X contained small amounts of nitrogen and oxygen elements. Moreover, heteroatom-doped FAC2 and HAC2 electrode materials shown excellent rate performance (84.1% and 75.0% capacitance retention at 20 A g-1, respectively). By comparison, the oxygen-rich hierarchical porous carbon (HAC2) shows higher specific capacitance and energy density and longer cycling performance. Nevertheless, carbon-rich hierarchical porous carbon (FAC2) indicates excellent rate performance. Biomass-derived heteroatom self-doped porous carbons are expected to become ideal active materials for high performance supercapacitor.

Efficient microwave absorber and supercapacitors derived from puffed-rice-based biomass carbon: Effects of activating temperature

Biomass-based carbon is gaining increasing attention because it presents a promising prospect for economic growth and social sustainable development. Moreover, it is an excellent medium for application in electromagnetic and electronic devices. Here, puffed-rice-based carbon is obtained at various activating temperatures, and when the hollow bulges on the carbon disappear, the morphology of the carbon changes into sheet-like structures. The R-800 sample displays the highest I_D/I_G value and demonstrates the best performance when used as both a microwave absorber and an electrode material. The minimum reflection loss (RL) and bandwidth for RL < -10 dB of the R-800 sample reach -72.1 dB and 13.2 GHz, respectively, and the bandwidth for RL < -20 dB is as large as 7.0 GHz, illustrating the widest bandwidth among the five carbon specimens. The multiple reflection effects and scattering, good impedance matching, and interfacial polarization synergistically enhance the microwave absorption performances of the sample. At 1 A g^-1, the specific capacitance of the R-800 sample reaches 117.2 F g^-1 and the capacitance retention remains at 85.3%. Moreover, a hybrid supercapacitor R-800//R-800 demonstrates an outstanding energy density of 15.23 Wh kg^-1, power density of 5739.43 W kg^-1, and high cycle stability (94.5% after 5000 cycles). This functionalized biomass carbon provides a promising media for constructing a bridge between sustainable development and biomass materials.

Enhanced Electrochemical Behavior of Peanut-Shell Activated Carbon/Molybdenum Oxide/Molybdenum Carbide Ternary Composites

Biomass-waste activated carbon/molybdenum oxide/molybdenum carbide ternary composites are prepared using a facile in-situ pyrolysis process in argon ambient with varying mass ratios of ammonium molybdate tetrahydrate to porous peanut shell activated carbon (PAC). The formation of MoO2 and Mo2C nanostructures embedded in the porous carbon framework is confirmed by extensive structural characterization and elemental mapping analysis. The best composite when used as electrodes in a symmetric supercapacitor (PAC/MoO2/Mo2C-1//PAC/MoO2/Mo2C-1) exhibited a good cell capacitance of 115 F g-1 with an associated high specific energy of 51.8 W h kg-1, as well as a specific power of 0.9 kW kg-1 at a cell voltage of 1.8 V at 1 A g-1. Increasing the specific current to 20 A g-1 still showcased a device capable of delivering up to 30 W h kg-1 specific energy and 18 kW kg-1 of specific power. Additionally, with a great cycling stability, a 99.8% coulombic efficiency and capacitance retention of ~83% were recorded for over 25,000 galvanostatic charge-discharge cycles at 10 A g-1. The voltage holding test after a 160 h floating time resulted in increase of the specific capacitance from 74.7 to 90 F g-1 at 10 A g-1 for this storage device. The remarkable electrochemical performance is based on the synergistic effect of metal oxide/metal carbide (MoO2/Mo2C) with the interconnected porous carbon. The PAC/MoO2/Mo2C ternary composites highlight promising Mo-based electrode materials suitable for high-performance energy storage. Explicitly, this work also demonstrates a simple and sustainable approach to enhance the electrochemical performance of porous carbon materials.

The preparation of porous carbon materials derived from bio-protic ionic liquid with application in flexible solid-state supercapacitors

Ionic liquids have attracted much more attentions for its wide application in catalyst, green solvents and carbon precursors. Herein, N/P co-doped porous carbon materials with developed pore structure were facilely prepared from the phosphoric acid protic ionic liquid of arginine (Arg[H₂PO₄]₂) and (NH₄)₂HPO₄. The former acted as the carbon precursor, heteroatom source and mesopore generator, while the latter worked as the activator which had great impact on the pore distribution and microstructure. The porous carbon materials were characterized by SEM, XRD, Raman and N₂ adsorption analysis in system, indicating that Arg-2-900 was promising electrode materials for supercapacitors. It exhibited high specific capacitance retention of 94% after 10000 cycles with stable electric double layer capacitors. The assembled symmetrical supercapacitors exhibited a wide voltage window in alkaline electrolyte and neutral aqueous electrolyte, displaying high energy density and power density, respectively. In addition, the solid-state supercapacitors were prepared and showed good flexibility after bending the flexible supercapacitor cell at different angles. The results demonstrated the successful synthesis of N/P co-doped porous carbon materials form Arg[H₂PO₄]₂ and broad application in wearable storage device.

One-step production of N-O-P-S co-doped porous carbon from bean worms for supercapacitors with high performance

In recent years, multi-heteroatom-doped hierarchical porous carbons (HPCs) derived from natural potential precursors and synthesized in a simple, efficient and environmentally friendly manner have received extensive attention in many critical technology applications. Herein, bean worms (BWs), a pest in bean fields, were innovatively employed as a precursor via a one-step method to prepare N-O-P-S co-doped porous carbon materials. The pore structure and surface elemental composition of carbon can be modified by adjusting KOH dosage, exhibiting a high surface area (S _BET) of 1967.1 m² g^-1 together with many surface functional groups. The BW-based electrodes for supercapacitors were shown to have a good capacitance of up to 371.8 F g^-1 in 6 M KOH electrolyte at 0.1 A g^-1, and good rate properties with 190 F g^-1 at a high current density of 10 A g^-1. Furthermore, a symmetric supercapacitor based on the optimal carbon material (BWPC_1/3) was also assembled with a wide voltage window of 2.0 V, demonstrating satisfactory energy density (27.5 W h kg^-1 at 200 W kg^-1) and electrochemical cycling stability (97.1% retention at 10 A g^-1 over 10 000 charge/discharge cycles). The facile strategy proposed in this work provides an attractive way to achieve high-efficiency and scalable production of biomass-derived HPCs for energy storage.